The atmosphere can be regarded as a heat engine converting solar heat into the mechanical energy of wind, which in turn generates waves on the surface of the sea, so that both wind and wave energy can readily be traced back to the solar input. Wind energy used to be a major source of power, but gave way to the much cheaper and more reliable source presented by coal. Looking to the future, we can certainly make much better windmills (15% efficiency was perhaps the best in the past) but the improvement in size/cost ratio with increasing size drives one to large structures. A preference for disaggregated supply is needed to put even medium sized aerogenerators into the running, and a house-by-house supply would require quite sizeable structures. Really big structures, especially on the favoured hill top sites, would raise environmental questions that might drive one to off-shore locations, though of course these may well involve increased costs. Vertical axis as well as horizontal axis machines are being studied. Isolated locations, where the competition is less severe, might offer the first chance of economic viability without going to very large sizes. Wave energy has the great merit of being dependent on a non-local supply. In particular, the longer waves with their high energy content may originate hundreds or even thousands of miles from the scene of exploitation, and so the system has a steadiness much greater than might be expected. Indeed, the U.K. is located in one of the World's most favourable positions. Engineering exploitation is made difficult by the need for the apparatus to survive the wildest conditions and by the fact that, in many devices, the input is a large force with small displacement, a form of power for which there is little practical experience in its utilization. A variety of devices are being supported so as to establish where we should concentrate our effort. The potential size of the resource and its seasonal phasing in line with demand make this a most essential field of renewable development.